Once you understand the 4Cs, a few finer points can help you choose an exceptional laboratory-grown diamond. None of these are reasons to worry; they're simply things an informed buyer checks.

As-grown vs post-growth treated

Some CVD diamonds receive a post-growth treatment (often high pressure and high temperature) to improve their colour. It's a common, permanent process. The report's comments will say whether the stone is "as grown" or shows indications of treatment.

  • Treated stones are perfectly durable and beautiful, and are often very good value.
  • As-grown stones appeal to buyers who prefer no treatment; they may cost a little more.

Choose what matters to you, as long as it's disclosed.

Fluorescence

Fluorescence is a glow under ultraviolet light. Most lab-grown diamonds show none or faint fluorescence. Some HPHT stones can briefly glow (phosphoresce) after UV exposure, and some CVD stones show a faint orange or reddish reaction under UV. In normal lighting you won't notice any of this. Only strong fluorescence can occasionally make a stone look slightly hazy in sunlight, so ask for a daylight video if the report shows "strong".

Strain and graining

CVD diamonds grow in layers, and some show internal strain patterns visible only under special polarised light. In rare cases, heavy graining can reduce transparency slightly. A well-graded stone with a good clarity grade and a crisp video won't have this problem.

Tints

Lower colour grades in lab-grown stones may lean slightly grey or brown rather than yellow; some HPHT stones can show a faint blue. The colour grade reflects this, but a daylight video is the best check.

"Looks cloudy"?

If a lab-grown diamond looks cloudy, it's usually dirt, which a quick clean fixes. If it's the stone itself, it points to clarity, graining or strong fluorescence, all of which a good report and video will reveal before you buy.

The practical takeaway

1. Read the comments on the report.
2. Ask for a daylight video.
3. Prioritise cut quality, then colour and clarity.

More in our 12-point checklist. Questions? Ask us.